1. Field of the Invention
The present invention is directed to a polymer, and in particular to a formulation of polyvinyl chloride for use in repairing or relining pipelines, such as for delivering water or gas under pressure, for gravity drain applications such as sanitary or storm sewer systems, or for utility conduit applications.
2. Description of Related Art
Conduit systems are used extensively throughout the world in order to transfer or convey material, such as water and other fluids, from location to location for distribution throughout the system. For example, extensive conduit systems are used to distribute water to both residences and businesses for use and further processes. Typically, such conduit or piping systems are located underground, as aboveground piping would be both unsightly and intrusive.
Typical water conduit systems transport material through pipe, e.g., cast iron, ductile iron, reinforced concrete, asbestos-cement, etc., buried underground with the branches extending in various directions in order to reach the end user. Normally, with age or for some other reason, the present piping fails and begins to leak, thereby reducing line pressure and unnecessarily allowing water to leak into the area surrounding the piping. Such leaks not only affect the system, but increase the processing costs of the supplier which, in turn, increases the end user costs. Therefore, these leaks must be quickly repaired and preventative measures taken to ensure that further leakage is prevented.
Due to the underground positioning of the conduit system, repairing a leaking pipe is particularly labor intensive and time consuming. Trenches must be dug along the pipeline to locate the leak and effectively repair it prior to putting the pipe back in service. Various lining systems have been developed according to the prior art in an attempt to seal a leaking pipe or a pipe that has fallen into disrepair, whether to repair a present crack or to preventatively ensure against future cracks or breaks.
In addition, when a smaller diameter pipe is pulled through a larger diameter pipe, the joints formed between sections of pipe must be sufficiently strong to withstand the forces associated with pulling the pipe. In other words, the joints must not break or lose their integrity.
In another example, a method of pipe installation has been developed, as disclosed in U.S. Pat. No. 5,794,662 to St. Onge et al., specifically directed to pressurized pipeline applications. The St. Onge patent is directed to a method of relining sewer lines, water lines or gas lines, and uses a segmented liner of reduced size relative to the pipe being relined. However, as opposed to merely leaving the small diameter liner conduit within the large diameter outer conduit, the method of the St. Onge patent uses heat and/or pressure to mold the reduced size pipe to the shape of the pipe being relined. In particular, the inner or liner conduit is a thermoplastic pipe, typically a polyvinyl chloride (PVC) pipe that, when exposed to heat or pressure, expands and molds against the inside of an existing conduit to effect the relining of it. This process allows for both the lining of the entire length of pipe or only a portion of it that is damaged, which is typically referred to as “spot repair.”
According to the St. Onge patent, once the length of the liner conduit is inserted into the existing or host conduit, the liner conduit is plugged at either end and exposed to steam under pressure to heat the liner conduit along its length and apply pressure, which urges it to expand and contact the interior walls of the surrounding host conduit. Once the liner conduit has fully expanded to conform to the interior surface of the existing conduit, it is cooled and the plugs are removed. The resulting expanded liner conduit conforms to the walls of the host conduit, thereby preventing any further leakage. Also, the method of the St. Onge patent requires only trenches to be dug at either end of the section to be repaired.
While the St. Onge patent represents an advance in the art of relining or repairing underground conduit systems, there is room in the art for additional improvements and advancements. One such area is in the type of material used to form the liner conduit. A commonly used material for manufacturing conduit and pipe as mentioned above is polyvinyl chloride.
It is known to use extruded PVC pipe in conduit systems. Certain thermoplastic pipe, in particular PVC pipe, when heated and exposed to pressure, can be expanded and molded against the inside of an existing or host pipe to effect relining thereof. Furthermore, it is possible to have joints between pipe segments and subject the joined pipes to the required heat and pressure with the resultant combination expanded and molded against the host pipe to be relined with the integrity of the joints being maintained. The pipe segments can be of traditional sections, easily installed due to the reduced diameter and merely appropriately sized once properly located.
Published standards for PVC pipe used in water lines are available (see for example PPI PVC Range Composition, Listing of Qualified Ingredients TR-2/2004, Plastics Pipe Institute, Washington, D.C., 2004) and provide lists of acceptable additives and ranges therefor that can be used. However, known combinations of additives do not work in the conduit expansion process. In particular, fusion joints formed between pipe sections either break on expansion or burst when exposed to in-line water pressure and/or are too weak to withstand the pull force applied as the PVC pipe is pulled through an existing conduit. More particularly, existing extruded PVC water pipes do not fuse to form fusion joints that are anywhere near as strong as the extruded pipe itself.
One example of a PVC formulation includes, in parts per hundred parts of resin: 100 PVC resin, 0.3-1.0 heat stabilizer, 0.4-1.5 calcium stearate, 0.6-1.5 paraffin wax, 0-0.3 polyethylene wax, 0.5-3.0 titanium dioxide, 0-5.0 calcium carbonate, 0-2.0 process aid and 0-5.0 colorant as recited in PPI PVC Range of Composition, Listing of Qualified Ingredients, published by the Plastics Pipe Institute. However, prior art PVC formulations that fall within the ranges set forth in this PPI standard do not appear to achieve the desired expansion or fusion joint strength properties required for PVC liner conduit utilized in relining and/or conduit expansion processes.
Thus, a need remains for the formulation of polyvinyl chloride that has excellent elastomeric and expandability properties and/or form fusion joints approaching the strength of the extruded PVC pipe itself, and that can be used for relining water mains, fire protection lines, gravity drain systems and utility conduit applications.